QUANTITATIVE MODELS OF DISEASE: The notion that an indicant (sign, symptom, laboratory finding, etc.) can be possessed in varying degrees is the basis for our current major effort to delineate diseases in quantitative terms. Our current work on the tetralogy of Fallot will shortly be completed and the logical next step is to apply the technique to a larger group of diseases with better and more accurate measurements and more patients. In addition we will continue our work in extending the circumstances in which discriminant analysis can be used. Currently such analyses are very vulnerable to errors of classification in the training sample. The new techniques to be developed will mitigate the seriousness of such errors by comparing the nominal classification with a statistical analysis. Current investigations which allow the identification of disease characteristics from fragmentary and irregularly collected data as well as making the best inferences of the disease state of individuals from available data will be continued. More use of the computer program for optimal estimation (MLE) of multiple regression when there is much missing data is expected. The costs of running this program have declined as improvements were made.